Thermolite vs Merino

I don't want to have to mess about with washing base layers differently to my normal clothes. It's all about having something you can just dash into your normal wash.

I don't think i'm quite clear on how the Merino layers work. They hold more moisture - does that mean that they take moisture away from your skin, or that they just get really sweaty?
(Actually, as an after-thought, t-shirts get sweaty when i ride in them but they don't feel weird or irritate my skin...so perhaps it's just the synthetic material against my skin that i don't like).

Do synthetic layers generally work better at getting sweat away from your skin?

I'm now thinking that it might be about buying a decent over layer, and just wearing a t-shirt underneath.

Yes generally, although this obviously depends on the synthetic in question, but put a super high end synthetic against super high end merino wool, compare wicking performance and the synthetic will win everytime.

Merino pulls moisture from the skin but holds more fluid than synthetics. But even when holding fluid it's warmer than synthetic

basically it fucking rules

go and look at some camping forums for more info

James has almost got it right here ^ assuming you don't have to take into account the windchill factor then yes it is warmer even when holding fluid, however if you are not planning on wearing a shell jacket over the top to prevent windchill, then you should wear a synthetic layer underneath which keeps the moisture off of your skin and in the merino instead, allowing fluid to continue to evaporate into the air without taking your bodyheat with it, as the synthetic layer is wicking moisture away from your skin faster than the merino on its own would.
Due to the nature of merino and the way it holds fluid, it will be more prone to windchill if you are not wearing a shell on top of it, or a synthetic underneath.
I find this warm enough most of the winter and only put a shell on when it gets really humid or is raining/exceptionally windy.